Can't give you the precise storage needed for the game but it won't change the fact that you don't have enough at the moment. Try cleaning the storage up and delete the apk after the install to get it back. Though, 3.6 GB should be enough.
I don't have any kind of online update module, so you are installing the whole game in one go. It may be inconvenient but it's the only option to install Yorna on mobile devices at the moment.